Fix inconsistency in date check

1. Although the regex checks deny any date past the year 2999, the convert2date function check still allowed any year except 9999. As there's no logical reason to expect any years >=3000 in OSM, mark them as bad too. (Reason: in the Dutch community we spotted some very strange years in the `start_date` tag of buildings)

2. Add some extra safety for the "~", "s" and " BC" year checks. If the string consists only of those characters it should be treated as an invalid date. (The check function returns True on empty strings due to the handling of e.g. `1920..`, so a string `~` would return True after stripping the `~`)

plugins/Date.py

@@ -49,7 +49,7 @@ def init(self, logger):
     def convert2date(self, string):
         try:
             date = dateutil.parser.parse(string, default=self.default_date)
-            if date.year != 9999:
+            if date.year < 3000:
                 return date
         except (ValueError, TypeError, OverflowError):
             pass
@@ -59,11 +59,11 @@ def check(self, string):
         if len(string) == 0:
             return True
         if string[0] == '~':
-            return self.check(string[1:])
+            return len(string) > 1 and self.check(string[1:])
         if string[-1] == 's':
-            return self.check(string[:-1])
+            return len(string) > 1 and self.check(string[:-1])
         if string[-3:] == ' BC' or string[-3:] == ' AD':
-            return self.check(string[:-3])
+            return len(string) > 3 and self.check(string[:-3])
         if len(string) == 4 and self.Year.match(string):
             return True
         if len(string) == 10 and (self.Day1.match(string) or self.Day2.match(string)):
@@ -111,7 +111,7 @@ def test(self):
 
         assert not a.node(None, {"date":"yes", "amenity":"clock"}), ("date=yes")
 
-        for d in ["yes", "XVI", "p", "0000", "9999", "Ca9", "1914..9999", "2014..Ca09"]:
+        for d in ["yes", "XVI", "p", "0000", "9999", "Ca9", "1914..9999", "2014..Ca09", "7000", "~"]:
             self.check_err(a.node(None, {"date":d}), ("date={0}".format(d)))
             self.check_err(a.way(None, {"date":d}, None), ("date={0}".format(d)))
             self.check_err(a.relation(None, {"date":d}, None), ("date={0}".format(d)))